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From: "robin" <robin_v@bigpond.com>
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Subject: Re: ONES COMPLEMENT
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Message-ID: <NDqvg.7682$tE5.5789@news-server.bigpond.net.au>
Date: Wed, 19 Jul 2006 13:41:01 GMT
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Date: 2006-07-19T13:41:01+00:00
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glen herrmannsfeldt wrote in message ...
>robin wrote:
>> glen herrmannsfeldt wrote in message ...
>
>(snip)
>
>>>Well, you want unsigned arithmetic to do multiple precision,
>>>which is harder if a machine only supplies ones complement.
>
>> In what way?
>> The arithmetic is done using fewer bits than word.
>> You have to do that with twos complement also.
>
>The bits resulting in an unsigned addition or subtraction operation are
>the same as for a twos complement operation, but the detection of
>overflow (or carry/borrow) is different.  If you can properly detect
>carry/borrow you can do it with all the bits in the word.

The CDC cybers did not provide that.

>> The arithmetic required is addition; and all values
>> manipulated are positive.  Results are the same in
>> machines supporting ones or twos complement
>> representation for negative values.
>
>Hmm.  If you can detect the end around carry

The CDC cyber did not provide that.

>you can generate
>the correct unsigned result, and so still use all the bits.
>This is not usually easy in an high-level language,

Naturally.

> but should
>be provided to the assembly programmer.

The CDC Cyber did not provide that.